A number of diverse methods of producing liquid and solid disperse aerosols are now in current use.
Thus, for instance, there is known a method of producing liquid disperse aerosols by virtue of ultrasound (cf. a textbook "Physical principles of ultrasonics" by O. K. Eknadiosiants, Moscow, Nauka Publishers, 1970 /in Russian/).
Carrying into effect this method involves feeding a stream (film) of liquid onto the oscillating element of a magnetostriction generator, i.e., supersonic-frequency oscillations are applied to the liquid. The effect of ultrasonic radiation results in that some individual drops of liquid get torn away from the crests of microwaves.
The method is instrumental in producing a narrow-disperse composition of the aerosol within a range of 1 to 4.8 .mu.m. However, the method fails to find extensive application as it is applicable for dispersing low-viscosity liquids only. Besides, practical application of the method involves the use of special highly expensive ultrasonic generators (the cost of ultrasound dispersing of a liquid is 3 to 5 times that of pneumatic or mechanical methods of dispersing).
According to the aerodynamic method of producing liquid disperse aerosols dispersing of a liquid is due to a dynamic contacting of a flow of liquid with a flow of gas (cf. a textbook "Spraying of liquids by atomizers" by L. A. Vitman, Moscow 1962; and a textbook "Liquid atomizers" by D. G. Pazhi and V. S. Galustov, Moscow 1979 /both in Russian/). The method is carried into effect in such a way that the stream of gas discharges from the nozzle at a velocity as high as 150 to 300 m/s, whereas the discharge velocity of the liquid is comparatively low. Thus, the higher the difference between the discharge velocities of both streams the higher the degree of dispersity of the liquid. As a result there are produced liquid disperse aerosols featuring a very broad range of sizes of dispersed liquid particles (from 1.0 to 100 .mu.m). However, the method involves a great deal of power to be consumed and fails to disperse high-viscosity liquids. Moreover, the method requires special liquid-handling pumps for liquid to feed.
One more prior-art method of producing liquid disperse aerosols by atomizing a liquid with a jet of gas in the presence of ferromagnetic solids is disclosed in USSR Inventor's Certificate No. 387,570. According to the method ferromagnetic solids are introduced into the liquid, whereupon the resultant mixture is passed through a zone of action of an alternating electromagnetic field, whereby the ferromagnetic solids, while travelling along the magnetic lines of force, break a continuous flow of liquid into a number of separate elements, which are then conveyed by a stream of the atomizing gas, subjected to secondary dispersing and are carried away.
However, dispersing a liquid by the above method is inevitably accompanied by partial entrainment of ferromagnetic solids together with the dispersed liquid. This imposes bad limitation upon the applicability of the method, as any presence of solid impurities is inadmissible in producing liquid disperse aerosols used in, say, medicine and veterinary sanitation. Low average degree of dispersity of the particles of the liquid being atomized, as well as a necessity of using complicated systems for establishing magnetic fields likewise restrict practical application of the method.
The most advanced of the heretofore known methods of producing solid disperse aerosols is the aerodynamic method, which is based on contacting a gas stream with the solid particles sucked into the outflowing portion of the gas stream, whereupon the solids are conveyed by the gas stream till colliding with an obstacle; while travelling the solids get pulverized by rubbing against one another and the walls of the apparatus (cf. "Air-stream mills" by V. I. Akunov, Moscow, 1967; "Disintegration processes in chemical industry" by P. M. Sidorenko, Moscow 1977 /both in Russian/). This method is carried into effect in air-stream mills featuring a flat, vertical, or counterflow grinding chamber.
The aerodynamic method of producing solid disperse aerosols is characterized by the following features:
1. Low impact impulse of the solids at the instance of their collision with the obstacle, which is accounted for by the fact that the solids are accelerated in an expanding gas stream, whereby the velocity of the solids drops and but low kinetic energy is imparted thereto. Thus, successful realization of the method depends upon the hardness of the initial stock being pulverized. PA1 2. High degree of attrition of penumoaccelerators used in counterflow aerodynamic atomization, as the solid disperse aerosol moves at a high speed with respect to the walls of the apparatus and proves to a highly efficient attrition abrasive. PA1 3. Realization of this method gives aerosols within a broad range of dispersity (particle size), in a majority of cases falling within 2 and 10 .mu.m, while occasionally the upper limit of dispersity reaches 30 .mu.m and the lower one, 1 .mu.m. This is owing to low impact energy at the instance of collision of the solids with the obstacle and to low probability for these solids to impinge upon one another.